redraw problem when moving or resizing window

Hello,

I have a matrox G550. Recently, I have upgraded my xorg installation.

 From :
Module mga: vendor="X.Org Foundation"
        compiled for 6.9.0, module version = 1.2.1
        Module class: X.Org Video Driver
        ABI class: X.Org Video Driver, version 0.8

To:
Module mga: vendor="X.Org Foundation"
        compiled for 7.2.0, module version = 1.4.6
        Module class: X.Org Video Driver
        ABI class: X.Org Video Driver, version 1.1

Since this upgrade, a serious problem appeared. When I drag or resize a 
direct rendering application window like glxgears, the image doesn't 
follow the window and stays in a static box on the desktop. I have tried 
with different kernel versions, different resolutions and bpp, the 
problem stays.

I have looked for this issue without success.

Anybody can help me to troubleshoot ?

Thank you

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